System for interrogating RFID transponders

ABSTRACT

Disclosed is a system for electromagnetic interrogation of RFID transponders including at least one RFID transponder, at least one so-called repeater RFID device and at least one RFID terminal, the at least one RFID terminal is configured to emit an interrogation signal towards the at least one repeater at a frequency F1, the at least one repeater is configured to repeat the interrogation signal with frequency F1 towards the at least one RFID transponder at a frequency F2 and the at least one RFID transponder is configured to emit a backscattered response signal at a frequency F3, the system being characterized in that the at least one repeater is configured to perform an exclusively analog frequency transposition from the frequency F1 to the frequency F2.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of radio frequencyidentification (RFID) in general, and specifically to a system forcommunication between a reader/interrogator and passive transponderslocated too far away from the reader/interrogator to be correctlyenergised by same. The present invention can be used in many fields suchas for product inventories in a warehouse or a store, and specifically,for example, in the field of distribution.

STATE OF THE ART

The scope of application of RFID technology has been growing for severalyears. Previously only known to the general public for its use inanti-theft technology, it is currently used in many industrial sectorsfor purposes of stock traceability and management, for example. Apassive transponder is a transponder which does not have its own powersource. Its power supply comes from an electromagnetic wave which itreceives via an antenna and which is then converted into a currentsource so as to power the functions of the transponder. Thecommunication protocols are regulated and standardised (EPC UHF Gen2standard and ISO 18000-6 standard). Thus, the generally encountered RFIDreaders/interrogators operate with passive transponders configured to bepowered and to communicate at a single frequency close to 900 MHz,specifically comprised between 865.6 MHz and 867.6 MHz in Europe andbetween 902 MHz and 928 MHz in the United States.

Technological developments have made it possible to reduce the size ofpassive transponders so that they can be included in small elements, forexample in textile elements in a simple seam, for example, or evenaffixed to documents. The increased use of this technology in sectorswith high product density involves certain constraints. Indeed,extensive infrastructure is sometimes required in order to be able tocommunicate with each of the transponders located in a storage space.The placement of readers/interrogators so as to cover a whole site canbecome expensive whenever the storage site is larger than 20 squaremeters. In order to reduce the installation and maintenance costs, anumber of solutions have been proposed. The main idea of these solutionsrelies on the use of what is referred to as a power node. A plurality oftypes of power nodes have been proposed.

U.S. Pat. No. 7,812,725 B2 discloses the use of power nodes arrangednear passive transponders. These nodes have their own power sources andremotely supply the RFID transponders in a certain space around same.This document proposes a so-called open-loop operating mode. Accordingto this operating mode of a system comprising a reader, a power node andan RFID transponder, the reader uses only its reader functions and notits interrogator functions, the power node remotely supplies the RFIDtransponder, which then backscatters a response that the reader iscapable of reading. In these conditions, the reading range of theresponse of the RFID transponder can be of the order of several tens ofmeters. The interrogation range of a standard reader is known to be onlyof the order of 5 to 8 meters.

Other solutions based on power nodes have a so-called distributedinterrogator function for generating an interrogation signal afterreceiving a control signal. These solutions indicate to the power nodeto execute certain commands and transforms on said interrogation signal.Thus, the power node demodulates the control signal and generates aninterrogation signal via a processor in order to be able interrogate theRFID transponder at the right frequency. The power node is controlled bythe reader/interrogator in order to make it perform certain actions.

These solutions include an energisation receiver for receiving a controlsignal from a reader, an energisation emitter for transmitting thereceived control signal as a repeated control signal to an RFIDtransponder and an energisation element for transmitting the energysignal as a separate energisation signal in addition to the controlsignal repeated to the RFID transponder in order to store the energy inthe RFID transponder so as to allow the backscattering signal to beemitted by the RFID transponder.

Thus, the solutions proposed in the prior art rely on the use of acomplex radio frequency device in order to power remotely and togenerate an interrogation signal, thus allowing the reader/interrogatorto be able to communicate with RFID transponders that are far away fromthe reader/interrogator.

In practice, this type of solution is found to have the followingdisadvantages:

-   -   considerable latency between the emission of an interrogation        signal by the reader/interrogator and the receipt by the        reader/interrogator of the response backscattered by the        transponder;    -   high installation and maintenance costs;

It would be useful to provide a solution to reduce at least one of thedrawbacks.

Moreover, it would be useful to further increase the performance ofthese solutions, in particular in terms of reading distance and/orreading success rates, while keeping the cost down.

The present invention aims to solve at least one of the goals mentionedabove.

SUMMARY OF THE INVENTION

According to one embodiment, the invention relates to a system forelectromagnetic interrogation of RFID transponders comprising at leastone RFID transponder, at least one so-called repeater RFID device and atleast one RFID terminal, the at least one RFID terminal is configured toemit an interrogation signal towards the at least one repeater at afrequency F1, the at least one repeater is configured to repeat saidinterrogation signal with frequency F1 towards the at least one RFIDtransponder at a frequency F2 and the at least one RFID transponder isconfigured to emit a backscattered signal at a frequency F3 in responseto receiving said interrogation signal transmitted by the at least onerepeater at the frequency F2. The at least one repeater is configured toperform an exclusively analog frequency transposition from the frequencyF1 to the frequency F2.

In an advantageous and optional manner, the exclusively analog frequencytransposition from the frequency F1 to the frequency F2 is carried outby mixing the analog interrogation signal or an analog signal which is afunction of the interrogation signal with a reference signal from areference local oscillator and in which the frequency is equal to F1−F2and/or F1+F2 so that signal output from the mixer has a frequency equalto F2.

According to one aspect, the present invention relates to a system forelectromagnetic interrogation of RFID transponders comprising at leastone RFID transponder and at least one RFID terminal comprising at leastone RFID reader, the at least one RFID terminal is configured to emit aninterrogation signal at a frequency F1, characterised in that the systemincludes at least one so-called repeater RFID device, in that the atleast one repeater is configured to repeat, at a frequency F2 differentfrom F1, said interrogation signal with frequency F1, said repeatedinterrogation signal with frequency F2 being intended for being receivedby the at least one RFID transponder, in that the at least one RFIDtransponder is configured to emit a backscattered response signal at afrequency F3 in response to receiving said repeated interrogation signaltransmitted by the at least one repeater at the frequency F2, andcharacterised in that in order to repeat at a frequency F2 saidinterrogation signal with frequency F1 the at least one repeater isconfigured to perform an exclusively analog frequency transposition fromthe frequency F1 to the frequency F2, the at least one repeatercomprising a generator of reference signals and the exclusively analogfrequency transposition comprising mixing said interrogation signal withfrequency F1 with a reference signal generated by said generator ofreference signals at a frequency F1−F2 and/or F1+F2.

The frequency transposition carried out in an analog manner has theadvantage that the interrogation signal is not demodulated and thenregenerated. Therefore, an analog frequency transposition makes itpossible to maintain quasi-synchronicity among the various signals ofthe RFID system. There is quasi-synchronicity between the interrogationsignals with frequency F0 and F1, the repeated interrogation signalswith frequency F2 and the backscattered response signals with frequencyF3. This quasi-synchronicity of the signals allows for bettersensitivity of the RFID reader so that the maximum distance for readingthe backscattered response of an RFID transponder is increased.

The invention thus makes it possible to improve the performance ofsystems for reading RFID transponders.

Furthermore, analog frequency transposition makes it possible to haverepeaters that are particularly robust and inexpensive to manufacture.It is thus possible to have a considerable number of repeaters which canthen be distributed more densely over the entire area to be covered soas to obtain high performance, while maintaining a very low cost for theinstallation.

The invention thus makes it possible to increase the communicationdistance between the transponders and a reader, while reducing the costof the installation, or at least keeping the cost low.

The repeater advantageously acts as a power node.

Furthermore, in the context of developing the present invention, itturns out that, in the known solutions, the processing of theinterrogation signal by the power node, which involves a processor andwhich includes a demodulation of the signal and the generation of a newsignal, accounts for a considerable portion of the latency of thesystem.

It should be noted here that latency is understood to be the timebetween the emission of an interrogation signal by thereader/interrogator and the receipt by the reader/interrogator of theresponse backscattered by the transponder.

By providing a repetition of the interrogation signal withoutdemodulating said signal and with a simple frequency transposition, theinvention makes it possible considerably to reduce the latency.

The performance of the systems for reading RFID transponders is thusimproved.

According to one aspect, the invention relates to a system forelectromagnetic interrogation of RFID transponders comprising at leastone RFID transponder, at least one so-called repeater RFID device and atleast one RFID terminal, the at least one repeater is configured torepeat an interrogation signal with frequency F1 from the at least oneRFID terminal and towards the at least one RFID transponder at afrequency F2 and the at least one RFID transponder is configured to emita backscattered signal at a frequency F3 in response to receiving saidinterrogation signal transmitted by the at least one repeater. An RFIDterminal includes at least one RFID reader, for example a standard RFIDreader, and an so-called add-on RFID device, configured to transpose aninterrogation signal with frequency F0 into an interrogation signal withfrequency F1 and to emit said interrogation signal towards the at leastone repeater at a frequency F1. The at least one repeater is configuredto perform a frequency transposition from the frequency F1 to thefrequency F2.

The use of a frequency F1 different from a frequency F2 makes itpossible to avoid the self-blindness phenomena inherent in the repeatersof a single frequency at the input and amplified at the output.

According to one aspect, the invention relates to a system forelectromagnetic interrogation of RFID transponders comprising at leastone RFID transponder, at least one so-called repeater RFID device and atleast one RFID terminal, the at least one repeater is configured torepeat an interrogation signal with frequency F1 from the at least oneRFID terminal and towards the at least one RFID transponder at afrequency F2 and the at least one RFID transponder is configured to emita backscattered signal at a frequency F3 in response to receiving saidinterrogation signal transmitted by the at least one repeater. The atleast one RFID terminal includes at least one RFID reader, typically astandard RFID reader, and an add-on RFID device, configured to transposean interrogation signal with frequency F0 into an interrogation signalwith frequency F1 and to emit said interrogation signal towards the atleast one repeater at a frequency F1.

Advantageously, this makes it possible to use a standard reader and thusto reduce the development costs while freely adapting the controlfrequency of the repeaters.

According to one aspect, the present invention relates to a repeater fora system for electromagnetic interrogation of RFID transponderscomprising at least one RFID transponder and at least one RFID terminalconfigured to emit an interrogation signal at a frequency F1, therepeater being configured to:

-   -   receive the interrogation signal at the frequency F1 emitted by        the at least one RFID terminal;    -   repeat, at a frequency F2 different from F1, said interrogation        signal with frequency F1, said repeated interrogation signal        with frequency F2 being intended for being received by the at        least one RFID transponder;

In order to repeat said interrogation signal with frequency F1 at afrequency F2, the at least one repeater is configured to perform anexclusively analog frequency transposition from the frequency F1 towardsthe frequency F2, the at least one repeater comprising a generator ofreference signals and the exclusively analog frequency transpositioncomprising mixing said interrogation signal with frequency F1 with areference signal generated by said generator of reference signals at afrequency F1−F2 and/or F1+F2.

The use of a repeater makes it possible to increase the communicationdistance with the RFID transponders; indeed, RFID transponders have avery small antenna compared with the antenna of the RFID terminal. Thus,the possibility of repeating an interrogation signal ensures a longerrange of communication within an RFID system.

In addition, the analog transposition carried out by the repeater allowsfor a further distance increase since, with the signals being mutuallyquasi-synchronous, the sensitivity of the RFID terminal is thusincreased.

The mixing of the signal with frequency F1 with the reference signal iscarried out so that the signal at the output of the mixer is equal toF2.

The repeater advantageously includes at least one add-on RFIDtransponder and at least one add-on antenna adapted to a servicefrequency F4, the add-on RFID transponder and the add-on antenna areconfigured to establish a service communication channel with frequencyF4 between the repeater and the RFID terminal so as to allow a dataexchange between the repeater by the RFID terminal, the frequency F4being different from the frequency F1.

Providing a service communication channel between the RFID terminal andthe repeater allows the repeater to be controlled from the RFIDterminal. This ensures a centralisation of the control of the repeaters.

In a highly advantageous manner, the use of an add-on RFID transponderassociated with the repeater makes it possible to use the nativefunctions of emitting interrogation signals and receiving backscatteredresponse signals of the RFID terminal.

Said associated add-on RFID transponder is advantageously configured toreceive instructions from the RFID terminal and the repeater isconfigured to perform at least one action as a function of saidinstruction, said instruction being taken from the following: activatingthe repeater, deactivating the repeater, verifying the level of chargeand cycles of the battery, controlling the frequency of the repeatedinterrogation signal with frequency F2, controlling the emission powerof the repeated interrogation signal with frequency F2, and controllingthe gain of the receiver of the interrogation signal with frequency F1.

In one possible configuration, the repeater includes more than onechannel for emitting the repeated interrogation signal with frequency F2and therefore more than one interrogation antenna configured to emit therepeated interrogation signal at the frequency F2. The RFID terminal canselect one channel among N possible channels in order to extend thespatial area for interrogating a single repeater so as to reduce thenumber of repeaters installed in a given system for a given space.

Advantageously, a single repeater can thus cover a very large surfacesimply by having a plurality of repetition channels operating at thefrequency F2.

In an optional and particularly advantageous manner, the control by theRFID terminal of the radiation of a given antenna connected to therepeater can allow scanning in two or three dimensions so as to locateRFID transponders at various locations of the facility from a singlerepeater in the case that it includes at least two antennas operating atthe emission frequency F2 of the repeated interrogation signal withfrequency F2.

BRIEF DESCRIPTION OF THE FIGURES

The goals and objectives as well as the characteristics and advantagesof the invention will better emerge from the detailed description of anembodiment of the latter which is illustrated by the following appendeddrawings wherein:

FIG. 1a shows a simplified diagram of the interactions between theelements of a system of the invention, according to one embodiment;

FIG. 1b shows a detailed diagram of the interactions between theelements of a system of the invention, according to one embodimentwherein the reader is a monostatic reader;

FIG. 2 shows the architecture, according to one embodiment of thepresent invention, of an RFID terminal with a monostatic reader;

FIG. 3 shows the architecture, according to one embodiment of thepresent invention, of a repeater.

FIG. 4 shows a detailed diagram of the interactions between the elementsof a system of the invention, according to one embodiment wherein thereader is a bistatic reader.

FIG. 5 shows the architecture, according to one embodiment of thepresent invention, of an RFID terminal with a bistatic reader;

The drawings are given as examples and are not limiting to theinvention. They are schematic illustrations in principle intended tofacilitate the understanding of the invention and are not necessarily tothe scale of practical applications.

DETAILED DESCRIPTION OF THE INVENTION

It is specified that, in the context of the present invention, the terms“RFID tag”, “RFID transponder” and the like define any device whichcomprises at least one antenna and an electronic microchip containingdata, and is configured to communicate with a reading device byelectromagnetic waves in order for said reader to be able to read saiddata contained in the electronic microchip.

It is specified that, in the context of the present invention, the terms“Passive RFID tag”, “Passive RFID transponder” and the like define anyRFID transponder which is powered by an electromagnetic wave, likewisedescribed as a remotely powered RFID transponder.

It is specified that, in the context of the present invention, the terms“Active RFID tag”, “Active RFID transponder” and the like define anyRFID transponder which is powered by its own energy source and/or alocal energy source, likewise described as a self-powered RFIDtransponder.

It is specified that, in the context of the present invention, the term“RFID reader”, “RFID interrogator” or the like define a deviceconfigured to communicate via electromagnetic waves having one or moreRFID devices, for example such as one or more RFID transponders.

It is specified that, in the context of the present invention, the term“RFID reader”, “standard RFID interrogator” or the like define a deviceconfigured to communicate via electromagnetic waves with one or moreRFID devices, for example such as one or more RFID transponders.

The terms “standard RFID reader”, “standard RFID interrogator” or thelike define an RFID reader communicating on the basis of regulated,standardised communication protocols (EPC UHF Gen2 standard and ISO18000-6 standard); this type of standard RFID reader is readilyavailable from most distributors of RFID readers.

Thus, according to the EPC UHF Gen2 standard and the ISO 18000-6standard, a “standard RFID reader” emits and reads signals withfrequencies comprised between 840 MHz and 960 MHz depending on thegeographical areas in which the UHF RFID system is used. Thus, in theUSA, the UHF band assigned to UHF applications is comprised between 902and 928 MHz, while it is comprised between 866 and 868 MHz in Europe.China authorises frequencies comprised between 840 and 844 MHz and Japanauthorises frequencies comprised between 952 MHz and 958 MHz.

It is specified that, in the context of the present invention, the term“standard monostatic RFID reader” or the equivalents thereof define astandard RFID reader comprising at least one single communication portconfigured to emit electromagnetic interrogation signals and to receiveelectromagnetic response signals.

It is specified that, in the context of the present invention, the terms“standard bistatic RFID reader” or the like define a standard RFIDreader comprising at least two communication ports, one configured toemit electromagnetic interrogation signals and the other configured toreceive electromagnetic response signals.

It is specified that, in the context of the present invention, the terms“quasi-synchronous signals” or the like define signals in which thefrequencies do not differ from one another by more than 500 Hz.

It should be noted that the present invention proposes a solution inwhich the power nodes are repeaters that do not have a processor andthat are configured to repeat the interrogation signals coming from animproved reader/interrogator. The proposed solution makes it possible inparticular to considerably reduce the latency as well as to improve thereading performance.

Before going into the details of the preferred embodiments, moreparticularly with reference to the figures, different options that theinvention may display preferentially but not restrictively, whereinthese options may be implemented either alone or in any combination, areenumerated hereunder:

-   -   Advantageously, the at least one RFID transponder is configured        to be powered by signals with frequency F2. This makes it        possible to use standard RFID transponders when the frequency F2        is close to 900 MHz.    -   Advantageously, said repeated interrogation signal with        frequency F2 emitted by the at least one repeater and received        by the at least one RFID transponder supplies enough energy to        said RFID transponder for the latter to emit said backscattered        response signal with frequency F3. This makes it possible to        power passive RFID transponders remotely with only the        interrogation signals repeated by the repeaters.    -   The generator of reference signals of the at least one repeater        advantageously includes a reference local oscillator in which        the frequency is equal to F1−F2 and/or F1+F2. This makes it        possible locally to have a reference signal which, once mixed        with the interrogation signal with frequency F1, produces an        repeated interrogation signal with frequency F2.    -   At least one add-on RFID transponder is advantageously        associated with the at least one repeater so as to allow control        of the at least one repeater by the at least one RFID terminal        via a communication channel comprising said add-on RFID        transponder associated with the at least one repeater. This        makes it possible to establish a service communication channel        between the RFID terminal and the repeater in order to be able        to control the repeater and to obtain information regarding, for        example, its status. The use of an add-on RFID transponder makes        it possible to use the communication systems already provided in        the RFID terminal to communicate without adding any additional        hardware.    -   The at least one standard RFID reader of the at least one RFID        terminal is advantageously configured to emit interrogation        signals with frequency F0, and the at least one RFID terminal        includes at least one add-on RFID device connected to the at        least one standard RFID reader and configured to transpose the        interrogation signals with frequency F0 emitted by the at least        one standard RFID reader into interrogation signals with        frequency F1 intended for being received by the at least one        repeater. This makes it possible, by simply adding this add-on        RFID device to any standard RFID reader, to implement the        present invention in an existing RFID system.    -   Advantageously, the at least one add-on RFID device is        configured to perform an exclusively analog transposition of the        interrogation signals with frequency F0 into interrogation        signals with frequency F1. This makes it possible to communicate        with RFID devices that do not have a standard communication        frequency.    -   Advantageously, the at least one standard RFID reader comprises        at least one common communication port, for receiving        backscattered response signals emitted by the at least one RFID        transponder and for emitting interrogation signals, to which the        at least one add-on RFID device is connected. This makes it        possible to use a standard monostatic RFID reader.    -   Advantageously, the at least one RFID terminal 100 includes at        least one of the following elements:        -   A standard monostatic UHF Gen2 RFID reader;        -   A circulator making it possible to isolate the response            signal backscattered by the at least one RFID transponder;        -   A generator of reference signals at the frequency F1−F0            and/or F1+F0 which, mixed with the interrogation signal at            the frequency F0, produces an interrogation signal with            frequency F1;        -   An analog mixer of the interrogation signal with frequency            F0 and the reference signal with frequency F1−F0 and/or            F1+F0;        -   An antenna configured to transmit the interrogation signal            with frequency F1 towards the at least one repeater;        -   A power amplifier powering the antenna, configured to emit            interrogation signals with frequency F1;        -   An antenna configured to receive the backscattered response            signal with frequency F3 coming from the at least one RFID            transponder;        -   An amplifier of the backscattered response signal with            frequency F3;        -   Optionally, a system for measuring the frequency offset            between the interrogation signal emitted by the at least one            standard RFID reader with frequency F0 and the response            signal backscattered by the at least one RFID transponder            with frequency F3;        -   A control unit managing the at least one RFID terminal.    -   Optionally, the terminal includes a service communication        channel allowing the at least one RFID terminal to communicate,        for emitting and receiving, with the at least one repeater via        an antenna adapted to the service frequency F4, the frequency F4        being different from the frequency F1.    -   Advantageously, the at least one RFID terminal includes at least        one of the following elements:        -   A standard bistatic UHF Gen2 RFID reader;        -   A generator of reference signals at the frequency F1−F0            and/or F1+F0 which, mixed with the interrogation signal at            the frequency F0, produces an interrogation signal with            frequency F1;        -   An analog mixer of the interrogation signal with frequency            F0 and the reference signal with frequency F1−F0 and/or            F1+F0;        -   An antenna configured to transmit the interrogation signal            with frequency F1 towards the at least one repeater;        -   A power amplifier powering the antenna, configured to emit            interrogation signals with frequency F1;        -   An antenna configured to receive the backscattered response            signal with frequency F3 coming from the at least one RFID            transponder;        -   An amplifier of the backscattered response signal with            frequency F3;        -   Optionally, a system for measuring the frequency offset            between the interrogation signal emitted by the at least one            standard RFID reader with frequency F0 and the response            signal backscattered by the at least one RFID transponder            with frequency F3;        -   A control unit managing the at least one RFID terminal.    -   Optionally, the terminal includes a service communication        channel allowing the at least one RFID terminal to communicate        with the at least one repeater via two antennas adapted to the        service frequency, one for receiving and one for emitting.    -   Advantageously, and without this being necessary, the reference        local oscillator is temperature-compensated. This makes it        possible to maintain the maximum reading performance of the        standard RFID reader, since the closer the frequencies F0, F2        and F3 are, the better the reading of the backscattered response        signals will be.    -   Advantageously and optionally, the at least one RFID terminal        includes a system for measuring the frequency offset between the        interrogation signal with frequency F0 and the backscattered        response signal with frequency F3 by the at least one RFID        transponder. This makes it possible, via the service        communication channel, to control the repeater so as to reduce        said frequency offset in order to maintain the best possible        reading performance.    -   Advantageously, the at least one RFID terminal includes a        service communication channel which allows the at least one RFID        terminal to communicate with the at least one repeater via at        least one antenna adapted to the service frequency F4. This        makes it possible to control the repeater.    -   Advantageously, the control unit of the at least one RFID        terminal is configured to send control data towards the at least        one repeater via the service communication channel. This makes        it possible to control the repeater.    -   Advantageously, the at least one repeater performs only one        frequency transposition. This makes it possible to obtain an        inexpensive repeater and to avoid self-blindness phenomena.    -   The at least one repeater advantageously includes at least one        of the following elements:        -   A receiving antenna configured to receive the interrogation            signal with frequency F1 emitted by the at least one RFID            terminal;        -   At least one emitting antenna configured to emit the            repeated interrogation signal with frequency F2 towards the            at least one RFID transponder;        -   The add-on RFID transponder configured to receive and emit            the service signals at the frequency F4.        -   A control unit managing the control data received from the            at least one RFID terminal via the service communication            channel at the frequency F4 and/or using Bluetooth Low            Energy;        -   A variable-gain amplifier controlled by the control unit;        -   A generator of reference signals at the frequency F1−F2            and/or F1+F2 which, mixed with received interrogation signal            at the frequency F1 produces a repeated interrogation signal            with frequency F2, and which is controlled by the control            unit;        -   A reference local oscillator in which the frequency has the            same value as the frequency of the reference local            oscillator of the at least one RFID terminal;        -   An analog mixer of the received interrogation signal with            frequency F1 with the reference signal with frequency F1−F2            and/or F1+F2, configured to output a repeated interrogation            signal with frequency F2;        -   A power amplifier powering the antenna, configured to emit            the interrogation signal with frequency F2;        -   An antenna configured to emit and receive the service            signals at the frequency F4;        -   At least one electric power source.    -   Advantageously, the frequencies F0, F2 and F3 are equal. This        makes it possible to improve the reading accuracy and        performance.    -   Advantageously, the frequencies F0, F2, F3 and F4 are equal.        This makes it possible to improve the reading accuracy and        performance.    -   Advantageously, said signals with frequencies F0, F2 and F3 are        quasi-synchronous; i.e., the frequency gap between the        frequencies F0, F2 and F3 is less than 500 Hz. This makes it        possible to improve the reading accuracy and performance.    -   A single signal is advantageously emitted by the at least one        repeater towards the at least one RFID transponder at a        frequency F2. This makes it possible to remotely power the RFID        transponder with the repeated interrogation signal with        frequency F2.    -   Advantageously, said repeated interrogation signal emitted by        the at least one repeater at a frequency F2 includes a carrier        which is used to supply energy to the at least one RFID        transponder and an amplitude modulation of said carrier, said        amplitude modulation being used to repeat said interrogation        signal emitted by the at least one RFID terminal with frequency        F1. This makes it possible to remotely power the RFID        transponder with the repeated interrogation signal with        frequency F2.    -   Advantageously, the frequency F1 is preferably comprised between        2.446 GHz and 2.454 GHz in Europe, advantageously between 2.4        GHz and 2.4835 GHz in the United States and preferably is equal        to 2.45 GHz.    -   Advantageously, the frequency F2 is comprised between 866 MHz        and 867 MHz in Europe and between 902 MHz and 928 MHz in the        United States.    -   Advantageously, the frequency F0 is comprised between 866 MHz        and 867 MHz in Europe and between 902 MHz and 928 MHz in the        United States.    -   At least one add-on RFID transponder is advantageously        associated with the repeater and provides a service        communication channel between the repeater and the at least one        RFID terminal. The use of an add-on RFID transponder makes it        possible to use the communication systems already provided in        the RFID terminal to communicate without adding any additional        hardware.    -   The service communication channel which allows the at least one        RFID terminal to communicate with the at least one repeater        advantageously includes at least one antenna adapted to the        service frequency F4.    -   Advantageously, the RFID terminal is configured so that the        interrogation signal with frequency F0 emitted by the standard        monostatic RFID reader transits via a high-isolation circulator,        passes through a directional coupler to seek the frequency F1,        is then mixed in an analog mixer with the reference signal with        frequency F1−F0 and/or F1+F0 so that, at the output of said        mixer, said interrogation signal has, as its frequency, the        frequency F1, and is then amplified and emitted by the RFID        terminal towards at least one repeater.    -   Advantageously, the RFID terminal is configured so that the        backscattered response signal with frequency F3 received by the        RFID terminal is first amplified and then transits via a        directional coupler to seek the frequency F3 before passing        through a high-isolation circulator so as to be separated from        the interrogation signals emitted by the standard RFID reader.    -   Advantageously, the RFID terminal is configured so that the        interrogation signal with frequency F0 emitted by the standard        bistatic RFID reader passes through a directional coupler to        seek the frequency F1, is then mixed in an analog mixer with the        reference signal with frequency F1−F0 and/or F1+F0 so that, at        the output of said mixer, said interrogation signal has, as its        frequency, the frequency F1, and is then amplified and emitted        by the RFID terminal towards at least one repeater.    -   Advantageously, the RFID terminal is configured so that the        backscattered response signal with frequency F3 received by the        RFID terminal is first amplified and then transits via a        directional coupler to seek the frequency F3.    -   The generator of reference signals of the at least one repeater        advantageously includes a reference local oscillator and the        reference local oscillator of the at least one repeater is        temperature-compensated so that the frequency thereof has the        same value as the frequency of the reference signal of the at        least one RFID terminal.    -   At least one add-on RFID transponder is advantageously        associated with the repeater and provides a service        communication channel between the repeater and the at least one        RFID terminal. This allows communication between the RFID        terminal and the repeater.    -   Said add-on RFID transponder is advantageously configured to        receive instructions contained in the control data of the RFID        terminal, and the repeater is configured to perform at least one        action as a function of said instruction, said instruction being        taken from the following: activating the repeater, deactivating        the repeater, verifying the level of charge and the cycles of at        least one electric power source of the repeater, controlling the        frequency of the repeated interrogation signal with frequency        F2, controlling the emission power of the repeated interrogation        signal with frequency F2, and controlling the gain of the        receiver of the interrogation signal with frequency F1. This        makes it possible to control the repeater by the RFID terminal.    -   The repeater advantageously has N>1 interrogation channels        configured to repeat interrogation signals with frequency F2,        each channel being connected to a separate antenna. This makes        it possible to extend the space of action of a single repeater.    -   Advantageously, said RFID transponder is configured to receive        instructions contained in the control data of the RFID terminal        and the repeater is configured to perform at least one action as        a function of said instruction, said instruction being the        activation of one interrogation channel at the frequency F2        among N available channels of the repeater. This makes it        possible to decide what area of the space covered by the        repeater is to be interrogated by the RFID terminal.    -   The repeater advantageously has at least one interrogation        antenna at the frequency F2, the radiation of which is        controlled by the at least one RFID terminal, allowing the at        least one RFID transponder to be located by scanning the        interrogation space. This allows the transponders to be located.    -   Advantageously, the frequency gap between the frequencies F0 and        F2, between the frequencies F0 and F3 and between the        frequencies F2 and F3 is lower than 1000 Hz, advantageously        lower than 500 Hz. This makes it possible to improve the reading        accuracy and performance.    -   The at least one add-on RFID device advantageously performs only        one frequency transposition. This makes it possible to        communicate with RFID devices having frequencies that are far        from 900 MHz.    -   The at least one add-on RFID device advantageously includes at        least one of the following elements:        -   A generator of reference signals at the frequency F1−F0            and/or F1+F0 which, mixed with interrogation signal at the            frequency F0, produces an interrogation signal with            frequency F1;        -   A generator of reference signals at the frequency F3−F0            and/or F3+F0 which, mixed with the backscattered response            signal at the frequency F3, produces a response signal with            frequency F0;        -   An analog mixer of the interrogation signal with frequency            F0 and the reference signal with frequency F1−F0 and/or            F1+F0;        -   An analog mixer of the backscattered response signal with            frequency F3 and the reference signal with frequency F3−F0            and/or F3+F0;        -   An antenna configured to transmit the interrogation signal            with frequency F1 towards the at least one repeater;        -   A power amplifier powering the antenna, configured to emit            interrogation signals with frequency F1;        -   An antenna configured to receive the backscattered response            signal with frequency F3 coming from the at least one RFID            transponder;        -   An amplifier of the backscattered response signal with            frequency F3;        -   Optionally, a system for measuring the frequency offset            between the interrogation signal emitted by the at least one            RFID reader with frequency F0 and the response signal            backscattered by the at least one RFID transponder with            frequency F3;        -   A control unit managing the at least one RFID terminal.        -   A service communication channel allowing the at least one            RFID terminal to communicate, for emitting and receiving,            with the at least one repeater via an antenna adapted to the            service frequency F4, the frequency F4 being different from            the frequency F1.    -   The generator of reference signals of the at least one add-on        RFID device advantageously includes a reference local oscillator        and the reference local oscillator of the at least one add-on        RFID device is temperature-compensated so that the frequency        thereof has the same value as the frequency of the reference        signal of the at least one repeater. This allows the repeater to        repeat the signal sent to the transponder in an analog manner.        This makes it possible to maintain the quasi-synchronicity        between certain signals.    -   The at least one RFID reader advantageously comprises at least        one common communication port for receiving backscattered        response signals emitted by the at least one RFID transponder        and for emitting interrogation signals to which the at least one        add-on RFID device is connected. This makes it possible to use        the add-on RFID device with a monostatic RFID reader.    -   Said interrogation signal emitted by the at least one add-on        RFID device at a frequency F1 advantageously includes an        amplitude modulation of a carrier, said amplitude being useful        for transmitting said interrogation signal emitted by the at        least one RFID reader with frequency F0. This makes it possible        to transmit an interrogation signal via the amplitude modulation        towards the at least one repeater.    -   The add-on RFID device is advantageously configured to perform a        frequency transposition of a signal with frequency F0 into a        signal with frequency F1, regardless of the type of modulation        of the signal with frequency F0. This makes it possible to carry        out the frequency transposition on any type of modulated signal.    -   A single signal is advantageously emitted by the at least one        add-on RFID device towards the at least one repeater at a        frequency F1. The repeater does not need to be powered; it has        its own power source. This makes it possible to reduce the        emission power of the RFID terminal and the emission time        thereof.    -   Advantageously, the frequencies F0 and F1 are different.    -   The generator of reference signals of the at least one add-on        RFID device advantageously includes a reference local oscillator        in which the frequency is equal to F1−F0 and/or F1+F0. This        makes it possible to transpose the frequency F0 to the frequency        F1 in an analog manner by mixing a reference signal with        frequency F1−F0 and/or F1+F0 with the interrogation signal with        frequency F0. This makes it possible to ensure the        quasi-synchronicity between the interrogation signal with        frequency F0 and the interrogation signal with frequency F1.    -   Advantageously, the RFID terminal is configured so that the        interrogation signal with frequency F0 emitted by the RFID        reader passes through a directional coupler to seek the        frequency F1, is then mixed in an analog mixer with the        reference signal with frequency F1−F0 and/or F1+F0 so that, at        the output of said mixer, said interrogation signal has, as its        frequency, the frequency F1, and is then amplified and emitted        by the RFID terminal towards at least one repeater.    -   Advantageously, the RFID terminal is configured so that the        backscattered response signal with frequency F3 received by the        RFID terminal transits via a directional coupler to seek the        frequency F3 before passing through a high-isolation circulator        so as to be separated from the interrogation signals emitted by        the RFID reader.    -   Advantageously, the frequency F0 is comprised between 866 MHz        and 867 MHz in Europe and between 902 MHz and 928 MHz in the        United States, and the frequency F1 is preferably comprised        between 2.446 GHz and 2.454 GHz in Europe, advantageously        between 2.4 GHz and 2.4835 GHz in the United States and        preferably is equal to 2.45 GHz.    -   The add-on RFID device is advantageously connected in a wired        manner to the at least one RFID reader.    -   The repeater advantageously includes at least one add-on RFID        transponder and at least one add-on antenna adapted to a service        frequency F4, the add-on RFID transponder and the add-on antenna        are configured to establish a service communication channel with        frequency F4 between the repeater and the at least one RFID        terminal so as to allow control of the at least one repeater by        the at least one RFID terminal, the frequency F4 being different        from the frequency F1, and the control data include at least one        instruction taken from the following: activating the repeater,        deactivating the repeater, verifying the level of charge and        cycles of at least one electric power source of the repeater,        controlling the frequency of the repeated interrogation signal        with frequency F2, controlling the emission power of the        repeated interrogation signal with frequency F2, and controlling        the gain of the receiver of the interrogation signal with        frequency F1.    -   The repeater advantageously includes the following elements:        -   A receiving antenna configured to receive said interrogation            signal with frequency F1 emitted by the at least one RFID            terminal;        -   At least one emitting antenna configured to emit the            repeated interrogation signal with frequency F2 towards the            at least one RFID transponder;        -   Said generator of reference signals at the frequency F1−F2            and/or F1+F2;        -   An analog mixer of said received interrogation signal with            frequency F1 and said reference signal with frequency F1−F2            and/or F1+F2, configured to output a repeated interrogation            signal with frequency F2;        -   A control unit managing said control data received from the            at least one RFID terminal via said service communication            channel at the frequency F4;        -   The add-on RFID transponder configured to receive and emit            the service signals at the frequency F4.        -   The add-on antenna configured to emit and receive the            service signals at the frequency F4.    -   The repeater advantageously has N>1 interrogation channels        configured to transmit the repeated interrogation signal with        frequency F2, each channel comprising a separate antenna, each        antenna being configured to emit a repeated interrogation signal        at the frequency F2.    -   Advantageously, the associated add-on RFID transponder is        configured to receive instructions contained in the control data        of the RFID terminal and the repeater is configured to perform        at least one action as a function of said instruction, said        instruction being the activation of an interrogation channel at        the frequency F2 among the N available channels of the repeater.    -   The radiation of the at least one interrogation antenna at the        frequency F2 is advantageously controlled by the at least one        RFID terminal via the service communication channel at the        frequency F4, allowing the at least one RFID transponder to be        located by scanning the interrogation space.    -   Advantageously, the frequency F1 is preferably comprised between        2.446 GHz and 2.454 GHz, advantageously between 2.4 GHz and        2.4835 GHz and preferably is equal to 2.45 GHz, the frequency F2        is comprised between 866 MHz and 867 MHz or between 902 MHz and        928 MHz, the frequency F0 is comprised between 866 MHz and 867        MHz or between 902 MHz and 928 MHz, the frequency F3 is        comprised between 866 MHz and 867 MHz or between 902 MHz and 928        MHz and the frequency F4 is comprised between 866 MHz and 867        MHz or between 902 MHz and 928 MHz.    -   The RFID reader is advantageously a bistatic UHF Gen2 RFID        reader, and the at least one RFID terminal includes the        following elements:        -   A generator of reference signals at the frequency F1−F0            and/or F1+F0 which, mixed with interrogation signal at the            frequency F0, produces an interrogation signal with            frequency F1;        -   An analog mixer of the interrogation signal with frequency            F0 and the reference signal with frequency F1−F0 and/or            F1+F0;        -   An antenna configured to transmit the interrogation signal            with frequency F1 towards the at least one repeater;        -   An antenna configured to receive the response signal with            frequency F3 coming from the at least one RFID transponder;        -   A system for measuring the frequency offset between the            interrogation signal emitted by the at least one RFID reader            with frequency F0 and the response signal backscattered by            the at least one RFID transponder with frequency F3;        -   A service communication channel allowing the at least one            RFID terminal to communicate with the at least one repeater            by emitting via a first antenna adapted to a service            frequency F4 and by receiving via a second antenna adapted            to a frequency F4.    -   The RFID reader is advantageously a monostatic UHF Gen2 RFID        reader, and the at least one RFID terminal includes the        following elements:        -   A circulator making it possible to isolate the response            signal backscattered by the at least one RFID transponder;        -   A generator of reference signals at the frequency F1−F0            and/or F1+F0 which, mixed with interrogation signal at the            frequency F0, produces an interrogation signal with            frequency F1;        -   An analog mixer of the interrogation signal with frequency            F0 and the reference signal with frequency F1−F0 and/or            F1+F0;        -   An antenna configured to transmit the interrogation signal            with frequency F1 towards the at least one repeater;        -   An antenna configured to receive the response signal with            frequency F3 coming from the at least one RFID transponder;        -   A system for measuring the frequency offset between the            interrogation signal emitted by the at least one RFID reader            with frequency F0 and the response signal backscattered by            the at least one RFID transponder with frequency F3;        -   A service communication channel allowing the at least one            RFID terminal to communicate, for emitting and receiving,            with the at least one repeater via an antenna adapted to the            service frequency F4.    -   The generator of reference signals of the at least one repeater        advantageously includes a reference local oscillator in which        the frequency is equal to F1−F2 and/or F1+F2 so as to provide        said repeated interrogation signal with frequency F2.    -   The repeater advantageously only performs the following steps:        amplifying the interrogation signal with frequency F1,        transposing the frequency F1 of the amplified interrogation        signal towards the frequency F2; amplifying the repeated        interrogation signal with frequency F2; and receiving and        executing control data received from the RFID terminal.    -   The add-on RFID device advantageously includes the following        elements:        -   A generator of reference signals at the frequency F1−F0            and/or F1+F0 which, mixed with interrogation signal at the            frequency F0, produces an interrogation signal with            frequency F1;        -   An analog mixer of the interrogation signal with frequency            F0 and the reference signal with frequency F1−F0 and/or            F1+F0;        -   An antenna configured to transmit the interrogation signal            with frequency F1 towards the at least one repeater;        -   An amplifier of the response signal with frequency F3;        -   A system for measuring the frequency offset between the            interrogation signal emitted by the at least one RFID reader            with frequency F0 and the response signal backscattered by            the at least one RFID transponder with frequency F3;    -   Advantageously, the RFID terminal is configured so that the        interrogation signal with frequency F0 emitted by the RFID        reader passes through a directional coupler to seek the        frequency F1, is then mixed in an analog mixer with the        reference signal with frequency F1−F0 and/or F1+F0 so that, at        the output of said mixer, said interrogation signal has, as its        frequency, the frequency F1, and is then amplified and emitted        by the RFID terminal towards at least one repeater, and the        backscattered response signal with frequency F3 received by the        RFID terminal transits via a directional coupler to seek the        frequency F3 before passing through a high-isolation circulator        so as to be separated from the interrogation signals emitted by        the RFID reader.    -   Advantageously, the frequency F1 is preferably comprised between        2.446 GHz and 2.454 GHz, advantageously between 2.4 GHz and        2.4835 GHz and preferably is equal to 2.45 GHz, the frequency F2        is comprised between 866 MHz and 867 MHz or between 902 MHz and        928 MHz, the frequency F0 is comprised between 866 MHz and 867        MHz or between 902 MHz and 928 MHz and the frequency F3 is        comprised between 866 MHz and 867 MHz or between 902 MHz and 928        MHz.    -   The RFID reader is advantageously a bistatic UHF Gen2 RFID        reader, and the at least one RFID terminal includes the        following elements:        -   A generator of reference signals at the frequency F1−F0            and/or F1+F0 which, mixed with interrogation signal at the            frequency F0, produces an interrogation signal with            frequency F1;        -   An analog mixer of the interrogation signal with frequency            F0 and the reference signal with frequency F1−F0 and/or            F1+F0;        -   An antenna configured to transmit the interrogation signal            with frequency F1 towards the at least one repeater;        -   An antenna configured to receive the response signal with            frequency F3 coming from the at least one RFID transponder;        -   A system for measuring the frequency offset between the            interrogation signal emitted by the at least one RFID reader            with frequency F0 and the response signal backscattered by            the at least one RFID transponder (300) with frequency F3;    -   The RFID reader is advantageously a monostatic UHF Gen2 RFID        reader, and the at least one RFID terminal includes the        following elements:        -   A circulator making it possible to isolate the response            signal backscattered by the at least one RFID transponder;        -   A generator of reference signals at the frequency F1−F0            and/or F1+F0 which, mixed with interrogation signal at the            frequency F0, produces an interrogation signal with            frequency F1;        -   An analog mixer of the interrogation signal with frequency            F0 and the reference signal with frequency F1−F0 and/or            F1+F0;        -   An antenna configured to transmit the interrogation signal            with frequency F1 towards the at least one repeater;        -   An antenna configured to receive the response signal with            frequency F3 coming from the at least one RFID transponder;        -   A system for measuring the frequency offset between the            interrogation signal emitted by the at least one RFID reader            with frequency F0 and the response signal backscattered by            the at least one RFID transponder with frequency F3;    -   The at least one repeater advantageously includes the following        elements:        -   A receiving antenna configured to receive said interrogation            signal with frequency F1 emitted by the at least one RFID            terminal;        -   At least one emitting antenna configured to emit the            repeated interrogation signal with frequency F2 towards the            at least one RFID transponder;        -   said generator of reference signals at the frequency F1−F2            and/or F1+F2;        -   An analog mixer of said received interrogation signal with            frequency F1 and said reference signal with frequency F1−F2            and/or F1+F2, configured to output a repeated interrogation            signal with frequency F2;    -   Advantageously, the at least one additional device includes a        generator of reference signals and the exclusively analog        frequency transposition includes mixing said interrogation        signal with frequency F0 with a reference signal generated by        said generator of reference signals at a frequency F1−F0 and/or        F1+F0 so as to supply said interrogation signal with frequency        F1.    -   The at least one add-on RFID device advantageously performs        only: a transposition from the frequency F0 of the interrogation        signal to the frequency F1, an amplification of the        interrogation signal with frequency F1, and an amplification of        the backscattered response signal with frequency F3.

In an RFID system, the standard RFID reader transmits anamplitude-modulated carrier to the RFID transponder. Since the RFIDtransponder is passive, the latter merely reflects the incident wavefrom the reader without modifying the frequency thereof. Said incidentwave energises the circuit of the RFID transponder so as to allow thememory thereof to be read. These data are then retransmitted in thebackscattered wave modulation.

As a consequence thereof, the standard RFID reader recovers the wavebackscattered by the RFID transponder, which advantageously has exactlythe same frequency but with an amplitude modulation containinginformation of the RFID transponder, in particular the memory contentsthereof.

The standard RFID reader performs a synchronous demodulation bymultiplying the signal received by reflection of the RFID transponder tothe local oscillator. Since the two signals have the same frequency, thebaseband transposition by said multiplication as well as low-passfiltering only make it possible to recover the information modulated bythe RFID transponder without the carrier.

Whenever any RFID element is sought to be inserted between theinterrogation signal of the standard RFID reader and the RFIDtransponder, there may be a loss of reading performance of the RFIDreader. This comes from the frequency offset which can take place whenan additional element is inserted between the interrogation signal ofthe standard RFID reader and the RFID transponder.

In order to benefit from the best performance of the RFID reader, it isimportant for the frequency of the interrogation signal of the standardRFID reader and the frequency of the backscattered response signal ofthe RFID transponder to be as similar as possible. Indeed, thisfrequency gap should not exceed 1 kHz in a carrier with a frequencycomprised between 866 MHz and 867 MHz in Europe and between 902 MHz and928 MHz in the United States. They do not need to be at exactly the samefrequency, but only within 1 ppm (parts per million), which is broadlyenough for an RFID system.

There are two operating modes for an RFID system, the “Open Loop” modeand the “Closed Loop” mode.

According to the open-loop mode, the standard RFID reader is only usedas a reader; it does not interrogate the RFID transponders. Therefore,in an open-loop mode, the transponders are only energised, either by theactual reader or by any other RFID device such as, for example, a powernode. Thus, no command is sent to the RFID transponders; they onlyreceive an energisation signal. The RFID transponders therefore merelyemit a backscattered signal. The reader then receives said backscatteredsignal.

According to the closed-loop mode, the standard RFID reader emits aninterrogation signal towards the RFID transponders. This signal can berelayed and/or repeated by one or more RFID devices in order to reachthe RFID transponders. Said interrogation signal includes a series ofinstructions which are then executed by the RFID transponders. Inresponse to this interrogation signal, the RFID transponders then emit abackscattered response signal towards the RFID reader. Thisbackscattered response signal can be relayed and/or repeated by RFIDdevices. According to this operating mode, the transponders receive aninterrogation signal and not only an energisation signal. This mode thenmakes it possible to communicate with the transponders according to theinternal configuration thereof: the reader interrogates and thetransponders respond.

According to one embodiment, the present invention includes the use of aso-called add-on RFID element or add-on RFID device connected in a wiredand/or wireless manner to a standard RFID reader. The combination of thestandard RFID reader and the add-on RFID device is referred to as RFIDterminal. This add-on RFID device ensures a transposition of thefrequency F0 of the interrogation signal emitted by the standard RFIDreader towards an unlicensed authorised frequency F1, for example suchas the 2.45 GHz ISM band. The frequency F0 is preferably comprisedbetween 866 MHz and 867 MHz in Europe and between 902 MHz and 928 MHz inthe United States. Then, the interrogation signal with frequency F1 istransmitted to a so-called repeater RFID device. The repeater has thesole function of repeating the interrogating signal from the RFIDterminal towards one or more RFID transponders after having carried outan analog frequency transposition of the interrogation signal. Thus, theinterrogation signal is received by the repeater at a frequency F1 andis repeated to one or more RFID transponders at a frequency F2. Afterreceiving said repeated interrogation signal with frequency F2, thetransponders are configured to emit a backscattered response at afrequency F3; F3 is advantageously equal to F2. Said backscatteredresponse signal with frequency F3 is then received by the RFID terminal.Advantageously, the frequency F3 is equal to the frequency F0. This isfollowed by a demodulation step, as mentioned above.

However, due to the analog frequency transposition from the frequency F1to the frequency F2, the repeater includes a generator of referencesignals comprising a reference local oscillator, advantageouslytemperature-compensated. This is different from that which is includedin the RFID reader, and a frequency offset can appear. As introducedbeforehand, this frequency offset can result in a loss of readingperformance. In order to correct this, a service communication channelis set up between the RFID terminal and the repeater. This servicecommunication channel enables, among others, an adjustment of thereference local oscillator of the repeater in order to reduce thefrequency offset between the frequency F3 and the frequency F0, when thefrequency F3 is equal to the frequency F2. This service communicationchannel is provided by a wired and/or wireless link, such as Bluetoothand/or RFID and/or any other communication system. In the case of RFIDcommunication between the RFID terminal and the repeater, thecommunication frequency F4 is advantageously equal to the frequency F0.

According to one embodiment of the present invention, the frequencies F2and F0 do not differ by more than 500 Hz, the interrogation signals withfrequency F0 and the interrogation signals with frequency F2 formingquasi-synchronous signals. For this purpose, temperature-compensated,high-stability local oscillators are embedded in the repeaters and thefrequencies are monitored and adjusted via the service communicationchannel at regular time intervals in order to compensate for any timedrift. The measurement is carried out in the RFID terminal by measuringthe frequency difference between the UHF signal emitted by the standardRFID reader at the frequency F0 and that received at the frequency F3 ofthe RFID transponders and thus of the repeater in question when thefrequency F2 is equal to the frequency F3. According to the measureddifference, a correction value is sent to the repeater via the servicecommunication channel. The extraction of the two frequencies is carriedout, for example, by means of directional couplers with very lowinsertion losses.

According to one advantageous embodiment, the interrogation signals withfrequency F0, the repeated interrogation signals with frequency F2 andthe backscattered response signals with frequency F3 arequasi-synchronous (i.e. the frequency difference between the frequenciesF0 and F2, between the frequencies F0 and F3 and between the frequenciesF2 and F3, is less than 500 Hz).

Thus, the present invention includes an RFID system which can operate ina closed loop with RFID transponders located at distances which do notallow the interrogation signal to be received without using repeaters.Advantageously, the present invention makes it possible to interrogateRFID transponders located at a distance of 30 meters from the RFIDterminal in free-field propagation conditions.

All this happens as if the standard RFID reader communicates directlywith the RFID transponders. The add-on RFID device and the network ofrepeaters, due to their simplicity, are transparent to normal operationsof RFID transponder interrogation by the standard RFID reader. Thecircuit for transposing the interrogation signal F0 to F1, thepropagation thereof from an emitting antenna at a frequency F1 of theRFID terminal towards the receiving antenna of the repeater separated by10 to 30 meters, followed by the transposition thereof by a simple mixerat a frequency F2, and the amplification in order to be radiated locallytowards the RFID transponders around the repeater only lengthen thetravel time by less than one microsecond (10⁻⁶ second).

When a device receives according to a receiving antenna a signal withfrequency F and emits according to an emitting antenna said same signalat the same frequency F after amplification, a so-called self-blindnessphenomenon can occur. This phenomenon consists of the receiving antennareceiving the amplified signal emitted by the emitting antenna. Indeed,with identical frequencies, the emitting antenna is configured toreceive a signal at the frequency F, and thus the amplified signal withfrequency F emitted by the emitting antenna can be received by thereceiving antenna. In this situation, the reception of the device isgreatly disrupted by the emission of the amplified signal from said samedevice. This phenomenon is similar to the Larsen effect which isgenerally known in the field of acoustics. To avoid this type ofproblem, it is necessary to resort to high isolation between thereceiving antenna and the emitting antenna, by greatly reducing theamplification gain of the signal, for example. A better solutionconsists of working with different receiving and emitting frequencies.

The frequency F2 is advantageously different from the frequency F1 inorder to solve the self-blindness problems inherent in the repeaters ofa single input frequency and amplified output frequency.

FIGS. 1a and 1b show the interactions that take place between thevarious elements of the present invention. The invention relates to anRFID terminal 100 comprising a commercially available standard RFIDreader 110 and an add-on RFID device 120. The RFID terminal 100 isconnected to a computer network via a wired and/or wireless system. Forexample, the RFID terminal 100 can be connected to a computer by anEthernet cable. The add-on RFID device 120 is an additional module forgenerating signals at a frequency F1 from signals with frequency F0,preferably amplitude modulated and advantageously according to RFID UHFstandards ISO 18000-6 and EPC Gen2.

According to one embodiment, the RFID terminal 100 includes threeantennas. The first antenna corresponds to the emission of at least oneinterrogation signal at a frequency F1. The frequency F1 is preferablycomprised between 2.4 GHz and 2.5 GHz, and advantageously between 2.4GHz and 2.4835 GHz, advantageously between 2.446 GHz and 2.454 GHz, andpreferably is equal to 2.45 GHz. The second antenna corresponds to thereception of at least one backscattered response signal from at leastone RFID transponder 300 at the frequency F3. Finally, the third antennacorresponds to the emission and the reception of control signals to andfrom at least one repeater 200 at a frequency F4. This servicecommunication channel is advantageously uncoupled from the add-on RFIDdevice 120 of the RFID terminal 100; thus, according to one embodimentand advantageously, the third antenna is directly connected to thestandard RFID reader 110.

According to one embodiment, the repeater 200 includes at least threeantennas. A first antenna corresponds to the reception of theinterrogation signal at the frequency F1 from the RFID terminal 100. Thesecond antenna corresponds to the repetition of the interrogation signalat the frequency F2 towards at least one RFID transponder 300. Finally,the third antenna corresponds to the service communication channel,which allows the emission and reception of signals at a frequency F4from and towards the RFID terminal 100.

Advantageously, the frequency F4 is equal to the frequency F0.

Advantageously, the frequency F0 is equal to the frequency F2.

Advantageously, the frequency F3 is equal to the frequency F0.

According to one embodiment, the RFID transponders 300 are standard,commercially available transponders, and the frequency F2 isadvantageously equal to the frequency F3.

FIG. 2 shows the architecture of an RFID terminal 100 according to oneembodiment of the present invention. The RFID terminal 100 includes acommercially available standard RFID reader 110 and an add-on RFIDdevice 120. The standard RFID reader 110 is a commercially availablestandard RFID reader which has at least two monostatic ports.

According to one embodiment, the first monostatic port is connected tothe first and second antennas of the RFID terminal 100 passing through ahigh-isolation circulator in order to separate the incoming signals fromthe outgoing signals.

According to one embodiment, the add-on RFID device 120 then performs afrequency conversion of the signals emitted and received by the RFIDterminal 100.

The second monostatic port is connected directly to the third antenna ofthe RFID terminal 100. The second monostatic port is then used as acommunication port for the service communication channel with therepeater 200.

According to one embodiment, the RFID terminal 100 includes a UHF Gen2Standard monostatic RFID reader 110. The term monostatic indicates thata single port receives and emits signals; the emitted signals arereferred to as Tx and the received signals as Rx.

According to one embodiment, the RFID terminal 100 includes a circulatorwhich makes it possible to isolate the response signal backscattered bythe RFID transponders 300.

According to one embodiment, the RFID terminal 100 includes a generatorof reference signals comprising or made up of a reference localoscillator, preferably temperature-compensated. Advantageously, thefrequency of said reference local oscillator is identical to thefrequency of the reference local oscillator included in the repeater200.

According to one embodiment, the RFID terminal 100 includes a generatorof reference signals at the frequency of 1.55 GHz which, mixed with theinterrogation signal at a frequency close to 900 MHz, produces aninterrogation signal transposed to 2.45 GHz.

According to one embodiment, the RFID terminal 100 includes a poweramplifier supplying an antenna at 2.45 GHz and capable of communicatingat a plurality of tens of meters from the repeaters 300.

According to one embodiment, the RFID terminal 100 includes an antenna2.45 GHz suitable for transmitting the interrogation signal towards therepeaters 200.

According to one embodiment, the RFID terminal 100 includes a system formeasuring the frequency offset between the signal emitted by thestandard RFID reader 110 and the signal backscattered by the RFIDtransponders 300 from the repeaters 200.

According to one embodiment, the RFID terminal 100 includes a servicecommunication channel allowing the RFID terminal 100 to communicate withthe repeaters 200 via an antenna adapted to the service frequency.

According to one embodiment, the RFID terminal includes a control unitmanaging the RFID terminal 100 and sending the control data towards therepeaters 200 via the service communication channel.

According to one embodiment, when an interrogation signal with frequencyF0 is emitted by the monostatic standard RFID reader 110, it transitsvia a high-isolation circulator in order to separate the receivedsignals from the emitted signals. Then, the interrogation signal withfrequency F0 passes through a directional coupler to seek the frequencyF1 before being mixed in the analog mixer with the reference signal withfrequency F1−F0 and/or F1+F0. At the output of said mixer, theinterrogation signal has, as its frequency, the frequency F1. Then, thisinterrogation signal with frequency F1 is amplified and the emitted bythe RFID terminal 100 towards at least one repeater 200.

According to one embodiment, when a backscattered response signal withfrequency F3 is received by the RFID terminal 100, it is first amplifiedand then transits via a directional coupler to seek the frequency F3before passing through a high-isolation circulator so as to be separatedfrom the interrogation signals emitted by the standard RFID reader 110.

According to one embodiment, in the case of a standard bistatic RFIDreader 110, the communication port for emitting interrogation signalsand the communication port for receiving backscattered response signalsare separate from one another and thus make it possible not to resort toa high-isolation circulator.

According to one embodiment, when an interrogation signal with frequencyF0 is emitted by the standard bistatic RFID reader 110, it passesthrough a directional coupler to seek the frequency F1 before beingmixed in an analog mixer with the reference signal with frequency F1−F0and/or F1+F0. At the output of said mixer, the interrogation signal has,as its frequency, the frequency F1. Then, this interrogation signal withfrequency F1 is amplified and the emitted by the RFID terminal 100towards at least one repeater 200.

According to one embodiment, when a backscattered response signal withfrequency F3 is received by the RFID terminal 100, it is first amplifiedand then transits via a directional coupler to seek the frequency F3.

FIG. 3 shows the architecture of a repeater 200 according to oneembodiment of the present invention. A repeater 200 includes at leastone antenna for receiving the interrogation signal with frequency F1.This antenna transmits the received signal to an analog mixer in orderto carry out the frequency transposition to the frequency F2. The analogmixer is connected to the generator of reference signals comprising thereference local oscillator in order to perform the analog frequencytransposition. Said reference signal is stabilised at the frequencyF1−F2 and/or F1+F2 by using the temperature-compensated reference localoscillator. A control unit controls the generator of reference signals.This control unit is also connected to an RFID transponder, of typeEM4325 for example; said RFID transponder is referred to as add-on RFIDtransponder associated with the repeater 200.

According to one embodiment, the repeater 200 includes at least oneelectric power source; said power source is advantageously arechargeable battery.

According to one embodiment, when an interrogation signal emitted by theRFID terminal 100 is received by the repeater 200, it passes firstthrough an analog gain amplifier before being mixed in an analog mixerwith the reference signal with frequency F1−F2 and/or F1+F2. Then, theinterrogation signal with frequency F2 is amplified before being emittedtowards at least one RFID transponder 300.

FIG. 4 shows a detailed diagram of the interactions between elements ofa system of the invention, according to one embodiment wherein thestandard RFID reader 110 is a standard bistatic RFID reader, and thearchitecture of an RFID terminal 100 with a standard bistatic RFIDreader 110.

FIG. 5 shows the architecture of an RFID terminal 100 with a standardbistatic RFID reader 110.

For the description of the various components and individual steps ofsaid FIGS. 4 and 5, reference can be made to the descriptions relativeto FIGS. 1b and 2, which use monostatic RFID readers 110.

The use of a standard bistatic RFID reader 110 has several advantages.In particular, it does away with the need to have a directional coupleron the side of the RFID terminal 100 in order to isolate the emittedsignal Tx from the received signal Rx. These signals are carried to thestandard bistatic RFID reader 110 via two separate communication portsand thus are much better isolated. Typically, a double circulator makesit possible to obtain 50 dB (decibels) of isolation.

Furthermore, this embodiment makes it possible to improve thesensitivity of the standard RFID reader 110. Typically, −100 dBm (dBm:power ratio in decibels (dB) between the measured power and onemilliwatt (mW)) is obtained for a standard bistatic RFID reader,compared with −80 dBm for a standard monostatic RFID reader. With this20 dB gain, a reading range of the RFID transponders 300 by the RFIDterminal 100 is obtained which is ten times higher in theory, passingfrom several tens of meters to several hundred meters with the sameinput power of the RFID transponders 300. The limiting factor is thusthe link between the RFID terminal 100 and the repeaters 200 at theadvantageous frequency of 2.45 GHz.

According to one embodiment, the control unit and the add-on RFIDtransponder associated with the repeater 200 exchange data. The controlunit sends, for example to the add-on RFID transponder, associated withthe repeater 200, data relating to the state of the repeater 200, forexample the battery level thereof, the operating state thereof(operating or stopped) and/or all other useful information to ensure thebest management of the network of repeaters 200. The add-on RFIDtransponder associated with the repeater 200 is connected to the thirdantenna of the repeater 200. Said antenna corresponds to the servicecommunication channel capable of receiving a control signal at afrequency F4 and of emitting a backscattered response signal at afrequency F4. The information exchanged by said service communicationchannel can be used, for example, to adjust the frequency F2 relative tothe frequency F0.

Advantageously, the add-on RFID transponder associated with the repeater200 is an active RFID transponder powered by the battery of the repeater200.

According to one embodiment, the power source of the repeater 200 comesfrom an accumulator which is charged from photovoltaic cells, forexample. Therefore, the repeater 200 is independent from any electricalconnection and has low maintenance requirements.

According to one embodiment, the repeater 200 has a battery and/or awired power supply.

According to one embodiment, the repeaters 200 do not have a unit forprocessing complex data. Only the recovery of surveillance data andbasic commands requires a basic local automaton.

According to one embodiment, the RFID terminal 100 can communicate withthe repeater 200 via the service communication channel through theadd-on RFID transponder associated with the repeater 200. The RFIDterminal 100 can thus collect data relating for example to the state ofcharge of the repeater 200, the amplification gain, the measurement ofthe receiving and/or emitting signals and/or the measurement of thelocal reference frequency.

According to one embodiment, the remote control of the repeaters 200 canbe carried out either by using an RFID transponder to send and receiveinformation from the repeaters 200 or by using one of the free ports ofthe standard RFID reader 110. For example, the memory of the BAPtransponder (EM4325) which can be accessed via RFID or by a wireddigital serial link allows the exchange in both directions between theRFID terminal 100 and the repeater 200. A small Bluetooth Low Energymodule operating at 2.45 GHz can also perform the same function.

The service communication channel is advantageously never active whenthe repeater 200 receives and/or emits one or more signals from and/ortowards the RFID terminal 100 and/or one or more RFID transponders 300.Thus, the service communication channel operating at the frequency F4 isnever active when signals with frequencies F0, F1, F2 and F3 are beingtransmitted and/or received. Therefore, no interference is possible.

According to one embodiment, the repeaters 200 include an antenna forreceiving at 2.45 GHz the interrogation signal sent by the RFID terminal100.

According to one embodiment, the repeaters 200 include a control unitmanaging the control data received from the RFID terminal 100 via theservice communication channel in RFID ISM band at a frequency close to900 MHz or in Bluetooth Low Energy.

According to one embodiment, the repeaters 200 include a variable-gainpreamplifier controlled by the control unit.

According to one embodiment, the repeaters 200 include atemperature-compensated frequency reference.

According to one embodiment, the repeaters 200 include a generator ofreference signals at the frequency of 1.55 GHz, for example, from thereference frequency adjusted by the control unit in order to be closestto the frequency F0 of the RFID terminal 100.

According to one embodiment, the repeaters 200 include a mixer foranalog transposition to the ISM band, at a frequency close to 900 MHz,of the signal received from the RFID terminal at 2.45 GHz by mixing witha reference local oscillator at 1.55 GHz, for example.

According to one embodiment, the repeaters 200 include a power amplifierwhich powers an antenna with a frequency near 900 MHz, which makes itpossible to interrogate the RFID transponders 300 with a maximumauthorised radiated power, controlled by the control unit.

According to one embodiment, the repeaters 200 include a receivingantenna adapted to the receiving band of the service signal with afrequency near 900 MHz and/or 2.45 GHz.

According to one embodiment, the repeaters 200 include a self-containedpower supply such as a battery or a storage battery, which can berecharged by one or more environmental energy sources, for example lightenergy.

According to one embodiment, the present invention includes repeaters200 that do not have a processor and are capable of repeating theinterrogation signals from an RFID terminal 100 without demodulating theinterrogation signals.

According to one embodiment, there is a latency of less than 1microsecond according to the system of the present invention: theinsertion of a repeater 200 into the transmission of an interrogationsignal towards the RFID transponder 300 is transparent from the point ofview of the UHF Gen2 protocol viewed by the RFID terminal 100, which canthen include a single commercially available standard RFID reader 110with an add-on RFID device 120 to emit the interrogation signals at afrequency F1, said frequency is preferably equal to 2.45 GHz, from asignal with frequency F0, said frequency is preferably advantageouslynear 900 MHz, and preferably equal to 866 MHz in Europe, amplitudemodulated according to RFID UHF standards ISO 18000-6 and EPC Gen2.

According to one embodiment, the system architecture proposed by thepresent invention makes it possible to update an existing RFIDinstallation by simply adding an add-on RFID device 120, which onlycontains what is necessary for transposing and amplifying the signal,which is monostatic for example, from an existing standard RFID reader110. The infrastructure cost is thus reduced to a central additionalmodule and to repeaters that are not powered by the mains, since they donot require powerful processing of on-board data.

According to one embodiment, the proposed architecture, in which therepeaters 200 are linked entirely without communication and power wires,allows straightforward installation with no modification of the premisesto be monitored. Only the one or more RFID terminals 100 whichcentralise the readings need to be connected to a computer network viaWi-Fi and/or Ethernet and to have an electric power source such as amains connection, for example. The repeaters 200, on the other hand, canoperate using batteries recharged by photovoltaic cells which aresensitive to the artificial light in the installation location, forexample.

According to one embodiment, the arrangement of the repeaters 200 can bechanged regularly at the expense of changes in the layout of theproducts in a ready-made garment shop, for example. The lack of cablesallows non-qualified personnel to move the repeaters 200 by severalmeters without having to reconfigure the installation.

According to one embodiment, the interrogation frequency F0 istransposed to a different unlicensed authorised frequency, for examplesuch as the ISM 2.45 GHz band by the add-on RFID device 120 of the RFIDterminal 100. This interrogation signal is transmitted to repeaters 200distributed in the space to be inventoried. Thus, the interferences atthe frequency F0 which are typical of standard RFID readers 110, or at afrequency near 900 MHz, for example, are reduced. Thus, the low levelsbackscattered by the RFID transponders 300 arrive at the UHF antenna ofthe RFID terminal 100 with a low noise level. In addition, the power ofthe signal at the output of the UHF RFID reader 110 does not need to behigh, since it no longer remotely powers the RFID transponders 300directly and is between 0 dBm and 30 dBm, advantageously between 10 dBmand 20 dBm and preferably between 10 and 18 dBm. These power levels makeit possible to operate the receiver of the standard RFID reader 110under the best possible conditions by minimising the parasitic level ofthe emission signal which is injected back into the receiver and whichreduces the dynamics and thus the sensitivity of the receiver.

According to one embodiment, the present invention relates to asynchronous or quasi-synchronous system between the emission of aninterrogation signal and the reception of a backscattered responsesignal. This synchronicity or quasi-synchronicity is necessary in orderto maintain the initial performance of the standard RFID reader 110.

According to one embodiment, the difference between the frequencies isless than 500 Hz between the frequency F2 of the repeaters 200 and thefrequency F0 of the standard RFID reader 110 of the RFID terminal 100 inthe case that the frequency F3 is equal to the frequency F2. For afrequency difference higher than 500 Hz reading performance reductionscan be perceived. Once the frequencies of the repeaters 200 are set,they remain stable over a period of several days, in particular by theimplementation of temperature-compensated local reference oscillators,which ensure stabilities of several ppm.

According to one embodiment, the interrogation signal repeated by therepeater 200 with frequency F2 consists of an amplitude modulation of anelectromagnetic carrier wave with frequency F2. This repeatedinterrogation signal with frequency F2 then acts as an energising wave,in addition to transmitting information to the RFID transponders 300.Said remote supply is configured to supply enough energy to the RFIDtransponders 300 for them to be able to emit a backscattered signaltowards the RFID terminal 100.

According to one embodiment, the repeater 200 includes a housing and theadd-on RFID transponder is rigidly connected to said housing.

According to one embodiment, the repeater 200 is rigidly connected tothe add-on RFID transponder which is associated with same.

According to one embodiment, the repeater 200 and the add-on RFIDtransponder which is associated with same are connected together in awired and/or wireless manner.

According to one specific embodiment, the repeater 200 can include aplurality of channels for repeating the interrogation signal, configuredto transmit interrogation signals repeated at the same frequency and/orat different frequencies.

According to a particularly advantageous embodiment, the repeater 200can include a plurality of channels for repeating the interrogationsignal, configured to transmit the repeated interrogation signals at thesame advantageous frequency F2.

According to said embodiment, each of these channels, of which there areN, for example, includes a separate antenna. Each antenna is configuredto emit a repeated interrogation signal at the frequency F2 towards theRFID transponders 300.

According to one advantageous embodiment, the N antennas are spatiallyseparated from one another. This makes it possible advantageously tocover a larger surface for repeating repeated interrogation signals withfrequency F2.

According to this embodiment, the RFID terminal 100 can select arepetition channel, in particular in order to repeat the interrogationsignal using the service communication channel with frequency F4. Thus,the RFID terminal 100 can decide which of the N antennas emits therepeated interrogation signal at the frequency F2.

This embodiment is particularly advantageous since it makes it possibleconsiderably to extend the spatial coverage of a single repeater 200. Bysimply deploying the N antennas in one space, a single repeater 200 iscapable of covering a surface which would require N repeaters 200comprising a single antenna.

This embodiment is therefore particularly advantageous in economicterms.

However, according to this embodiment, the radiation of each antenna canbe controlled from the RFID terminal 100 so as to be able to locate, intwo dimensions and/or three-dimensions, an RFID transponder 300 arrangedin the space covered by the repeater 200 and the antennas thereof.

For example, the position of the RFID transponder 300 can be deduced bymeasuring the response time between the emission of the interrogationsignal and the reception of the response signal backscattered by saidRFID transponder 300, according to at least two and/or three differentantennas so as to be able to triangulate the position of the RFIDtransponder 300.

According to one embodiment, it is also possible to locate an RFIDtransponder 300 using a plurality of repeaters 200 distributed accordingto the space in which said RFID transponder 300 is arranged.

The use of the add-on RFID device 120 makes it possible, by simplyadding said module to a standard RFID reader 110, for the latter tocommunicate at various frequencies according to the configuration of theadd-on RFID device 120. Thus, it is advantageously possible to integratea solution based on a network of power nodes, or repeaters, in apre-existing RFID environment by simply adding said add-on RFID device120 to the standard RFID readers 110 already in place in order to allowcommunication according to various frequencies.

The add-on RFID device 120 is connected to the standard RFID reader 110in a wired and/or wireless manner. This ensures a frequencytransposition of all signals emitted by the standard RFID reader 110according to the configuration thereof.

Likewise, if need be, the add-on RFID device 120 transposes all thereceived signals according to the configuration thereof beforeretransmission to the standard RFID reader 110.

According to one specific embodiment, the add-on RFID device 120 isconfigured to transpose, in an optionally analog manner, a backscatteredresponse signal with frequency F3, emitted by an RFID transponder 300for example, into a backscattered response signal with frequency F0intended for the standard RFID reader 110 contained with the add-on RFIDdevice 120 in the RFID terminal 100.

The add-on RFID device 120 can be applied to any type of standard RFIDreader 110, whether monostatic or bistatic. The installation thereof ona standard RFID reader 110 is carried out, for example, by a singlewired connection at the communication ports of the standard RFID reader110.

According to one embodiment, the add-on RFID device 120 is configured toperform an exclusively analog frequency transposition.

According to one embodiment, the add-on RFID device 120 is configured toperform a frequency transposition of a signal with frequency F0 into asignal with frequency F1, regardless of the type of modulation of thesignal with frequency F0.

The invention is not limited to the embodiments described above andextends to all the embodiments covered by the claims.

The invention claimed is:
 1. A system for electromagnetic interrogationof RFID transponders, the system comprising: at least one RFIDtransponder; at least one RFID terminal comprising at least one RFIDreader, the at least one RFID terminal being configured to emit aninterrogation signal at a frequency F1; and at least one repeater RFIDdevice configured to repeat, at a frequency F2 different from F1, saidinterrogation signal with frequency F1, said repeated interrogationsignal with frequency F2 being intended for being received by the atleast one RFID transponder, wherein the at least one RFID transponder isconfigured to emit a backscattered response signal at a frequency F3 inresponse to receiving said repeated interrogation signal, in order torepeat, at a frequency F2, said interrogation signal with frequency F1,the at least one repeater RFID device is configured to perform anexclusively analog frequency transposition from the frequency F1 to thefrequency F2, the at least one repeater RFID device comprising agenerator of reference signals and the exclusively analog frequencytransposition comprising mixing said interrogation signal with frequencyF1 with a reference signal generated by said generator of referencesignals at a frequency F1-F2 and/or F1+F2 to provide said repeatedinterrogation signal with frequency F2, and the generator of referencesignals of the at least one repeater RFID device includes a referencelocal oscillator in which the frequency is equal to F1−F2 and/or F1+F2to provide the repeated interrogation signal with frequency F2.
 2. Thesystem according to claim 1, wherein the repeater RFID device includesat least one add-on RFID transponder and at least one add-on antennaadapted to a service frequency F4, wherein the add-on RFID transponderand the add-on antenna are configured to establish a servicecommunication channel with frequency F4 between the repeater RFID deviceand the RFID terminal to allow control of the repeater by the RFIDterminal, the frequency F4 being different from the frequency F1, andwherein the control data include at least one instruction taken from thefollowing: activating the repeater RFID device, deactivating therepeater RFID device, verifying the level of charge and cycles of atleast one electric power source of the repeater RFID device, controllingthe frequency of the repeated interrogation signal with frequency F2,controlling an emission power of the repeated interrogation signal withfrequency F2, and controlling a gain of a receiver of the interrogationsignal with frequency F1.
 3. The system according to claim 2, whereinthe at least one repeater includes at least the following elements: areceiving antenna configured to receive said interrogation signal withfrequency F1 emitted by the at least one RFID terminal, at least oneemitting antenna configured to emit the repeated interrogation signalwith frequency F2 towards the at least one RFID transponder, saidgenerator of reference signals at the frequency F1−F2 and/or F1+F2, ananalog mixer of said received interrogation signal with frequency F1 andsaid reference signal with frequency F1−F2 and/or F1+F2, configured toperform said mixing and to output said repeated interrogation signalwith frequency F2, a control unit managing said control data receivedfrom the at least one RFID terminal via said service communicationchannel at the frequency F4, the add-on RFID transponder configured toreceive and emit service signals at the frequency F4, and an add-onantenna configured to emit and receive service signals at the frequencyF4.
 4. The system according to claim 1, wherein the at least onerepeater RFID device only performs the following steps: amplifying theinterrogation signal with frequency F1, transposing the frequency F1 ofthe amplified interrogation signal towards the frequency F2, amplifyingthe repeated interrogation signal with frequency F2, and receiving andexecuting control data received from the RFID terminal.
 5. The systemaccording to claim 1, wherein the at least one RFID reader of the atleast one RFID terminal is configured to emit interrogation signals withfrequency F0, and wherein the at least one RFID terminal includes atleast one add-on RFID device, connected to the at least one RFID readerand configured to transpose the interrogation signals with frequency F0emitted by the at least one RFID reader into the interrogation signalswith frequency F1 intended for being received by the at least onerepeater RFID device.
 6. The system according to claim 5, wherein the atleast one add-on RFID device is configured to perform an exclusivelyanalog transposition of the interrogation signals with frequency F0 intointerrogation signals with frequency F1.
 7. The system according toclaim 5, wherein said RFID reader is a monostatic UHF Gen2 RFID reader,and wherein the at least one RFID terminal includes the followingelements: a circulator making it possible to isolate the response signalbackscattered by the at least one RFID transponder, a generator ofreference signals at the frequency F1−F0 and/or F1+F0 which, mixed withinterrogation signal at the frequency F0, produces an interrogationsignal with frequency F1, an analog mixer of the interrogation signalwith frequency F0 and the reference signal with frequency F1−F0 and/orF1+F0, an antenna configured to transmit the interrogation signal withfrequency F1 towards the at least one repeater RFID device, an antennaconfigured to receive the response signal with frequency F3 coming fromthe at least one RFID transponder, and a service communication channelallowing the at least one RFID terminal to communicate, for emitting andreceiving, with the at least one repeater via an antenna adapted to theservice frequency F4, the frequency F4 being different from thefrequency F1.
 8. The system according to claim 7, wherein the at leastone RFID reader comprises at least one common communication portconfigured to receive response signals emitted by the at least one RFIDtransponder and to emit interrogation signals with which the at leastone add-on RFID device is connected.
 9. The system according to claim 8,wherein the RFID terminal is configured so that the interrogation signalwith frequency F0 emitted by the RFID reader transits via ahigh-isolation circulator, then passes through a directional coupler toseek the frequency F1, is then mixed in an analog mixer with thereference signal with frequency F1−F0 and/or F1+F0 so that, at theoutput of said mixer, said interrogation signal has, as its frequency,the frequency F1, and is then amplified and emitted by the RFID terminaltowards at least one repeater.
 10. The system according to claim 8,wherein the RFID terminal is configured so that the backscatteredresponse signal with frequency F3 received by the RFID terminal is firstamplified and then transits via a directional coupler to seek thefrequency F3 before passing through a high-isolation circulator to beseparated from the interrogation signals emitted by the RFID reader. 11.The system according to claim 7, wherein said generator of referencesignals of the at least one RFID terminal includes a reference localoscillator, and wherein said reference local oscillator of the at leastone RFID terminal is temperature-compensated.
 12. The system accordingto claim 7, wherein the at least one RFID terminal includes a system formeasuring the frequency offset between the interrogation signal withfrequency F0 and the backscattered response signal with frequency F3 bythe at least one RFID transponder.
 13. The system according to claim 7,wherein the frequency gap between the frequencies F0 and F2, between thefrequencies F0 and F3, and between the frequencies F2 and F3 is lowerthan 1000 Hz, advantageously lower than 500 Hz.
 14. The system accordingto claim 7, wherein the frequencies F0, F2, F3, and F4 are equal. 15.The system according to claim 7, wherein the frequency F1 is preferablycomprised between 2.446 GHz and 2.454 GHz, advantageously between 2.4GHz and 2.4835 GHz and preferably is equal to 2.45 GHz, wherein thefrequency F2 is comprised between 866 MHz and 867 MHz or between 902 MHzand 928 MHz, wherein the frequency F0 is comprised between 866 MHz and867 MHz or between 902 MHz and 928 MHz, wherein the frequency F3 iscomprised between 866 MHz and 867 MHz or between 902 MHz and 928 MHz,and wherein the frequency F4 is comprised between 866 MHz and 867 MHz orbetween 902 MHz and 928 MHz.
 16. The system according to claim 5,wherein said RFID reader is a bistatic UHF Gen2 RFID reader, and whereinthe at least one RFID terminal includes the following elements: agenerator of reference signals at the frequency F1−F0 and/or F1+F0which, mixed with interrogation signal at the frequency F0, produces aninterrogation signal with frequency F1, an analog mixer of theinterrogation signal with frequency F0 and the reference signal withfrequency F1−F0 and/or F1+F0, an antenna configured to transmit theinterrogation signal with frequency F1 towards the at least one repeaterRFID device, an antenna configured to receive the response signal withfrequency F3 coming from the at least one RFID transponder, and aservice communication channel allowing the at least one RFID terminal tocommunicate with the at least one repeater RFID device configured toemit via a first antenna adapted to a service frequency F4, and toreceive via a second antenna adapted to a frequency F4, the frequency F4being different from the frequency F1.
 17. The system according to claim16, wherein the RFID terminal is configured so that the interrogationsignal with frequency F0 emitted by the RFID reader passes through adirectional coupler to seek the frequency F1, is then mixed in an analogmixer with the reference signal with frequency F1−F0 and/or F1+F0 sothat, at the output of said mixer, said interrogation signal has, as itsfrequency, the frequency F1, and is then amplified and emitted by theRFID terminal towards the at least one repeater RFID device.
 18. Thesystem according to claim 16, wherein the RFID terminal is configured sothat the backscattered response signal with frequency F3 received by theRFID terminal is first amplified and then transits via a directionalcoupler to seek the frequency F3.
 19. The system according to claim 1,wherein said repeated interrogation signal with frequency F2 emitted bythe at least one repeater RFID device and received by the at least oneRFID transponder supplies enough energy to said RFID transponder for theRFID transponder to emit said backscattered response signal withfrequency F3.
 20. The system according to claim 1, wherein said repeatedinterrogation signal emitted by the at least one repeater RFID device ata frequency F2 includes a carrier configured to supply energy to the atleast one RFID transponder and an amplitude modulation of said carrier,said amplitude modulation being used to repeat said interrogation signalemitted by the at least one RFID terminal with frequency F1.
 21. Arepeater for a system including at least one RFID transponder and atleast one RFID terminal configured to emit an interrogation signal at afrequency F1, the repeater comprises: one or more processors configuredto receive the interrogation signal at the frequency F1 emitted by theat least one RFID terminal, repeat, at a frequency F2 different from F1,said interrogation signal with frequency F1, said repeated interrogationsignal with frequency F2 being intended for being received by the atleast one RFID transponder, and in order to repeat said interrogationsignal with frequency F1 at a frequency F2, perform an exclusivelyanalog frequency transposition from the frequency F1 to the frequencyF2, wherein the at least one repeater comprises a generator of referencesignals and the exclusively analog frequency transposition comprisingmixing said interrogation signal with frequency F1 with a referencesignal generated by said generator of reference signals at a frequencyF1−F2 and/or F1+F2, and the generator of reference signals of the atleast one repeater includes a reference local oscillator in which thefrequency is equal to F1−F2 and/or F1+F2 to provide the repeatedinterrogation signal with frequency F2.
 22. The repeater according toclaim 21, further comprising at least one add-on RFID transponder and atleast one add-on antenna adapted to a service frequency F4, wherein theadd-on RFID transponder and the add-on antenna are configured to receivecontrol data at a frequency F4, emitted by the at least one RFIDterminal to allow control of the at least one repeater by the at leastone RFID terminal, the frequency F4 being different from the frequencyF1, and wherein the control data include at least one instruction takenfrom the following: activating the repeater, deactivating the repeater,verifying the level of charge and cycles of at least one electric powersource of the repeater, controlling the frequency of the repeatedinterrogation signal with frequency F2, controlling the emission powerof the repeated interrogation signal with frequency F2, and controllinga gain of a receiver of the interrogation signal with frequency F1. 23.The repeater according to claim 22, further comprising: a receivingantenna configured to receive said interrogation signal with frequencyF1 emitted by the at least one RFID terminal; at least one emittingantenna configured to emit the repeated interrogation signal withfrequency F2 towards the at least one RFID transponder; the generator ofreference signals at the frequency F1−F2 and/or F1+F2; an analog mixerof said received interrogation signal with frequency F1 and saidreference signal with frequency F1−F2 and/or F1+F2, configured to outputa repeated interrogation signal with frequency F2; a control unitmanaging said control data received from the at least one RFID terminal(100); an add-on RFID transponder configured to receive and emit servicesignals at the frequency F4; and the add-on antenna configured to emitand receive service signals at the frequency F4.
 24. The repeateraccording to claim 21, wherein the repeater has N>1 interrogationchannels configured to transmit the repeated interrogation signal withfrequency F2, each channel comprising a separate antenna, each antennabeing configured to emit an interrogation signal repeated at thefrequency F2.
 25. The repeater according to claim 24, wherein anassociated add-on RFID transponder is configured to receive instructionscontained in the control data of the RFID terminal and the repeater isconfigured to perform at least one action that is a function of saidinstruction, said instruction being the activation of an interrogationchannel at the frequency F2 among the N available channels of therepeater.
 26. The repeater according to claim 21, wherein the radiationof the at least one interrogation antenna at the frequency F2 iscontrolled by the at least one RFID terminal via the control data,allowing at least one RFID transponder to be located by scanning theinterrogation space around the repeater.
 27. A system forelectromagnetic interrogation of RFID transponders, the systemcomprising: at least one RFID transponder; at least one RFID terminalcomprising at least one RFID reader, the at least one RFID terminalbeing configured to emit an interrogation signal at a frequency F1; andat least one repeater RFID device configured to repeat, at a frequencyF2 different from F1, said interrogation signal with frequency F1, saidrepeated interrogation signal with frequency F2 being intended for beingreceived by the at least one RFID transponder, wherein the at least oneRFID transponder is configured to emit a backscattered response signalat a frequency F3 in response to receiving said repeated interrogationsignal, in order to repeat, at a frequency F2, said interrogation signalwith frequency F1, the at least one repeater RFID device is configuredto perform an exclusively analog frequency transposition from thefrequency F1 to the frequency F2, the at least one repeater RFID devicecomprising a generator of reference signals and the exclusively analogfrequency transposition comprising mixing said interrogation signal withfrequency F1 with a reference signal generated by said generator ofreference signals at a frequency F1−F2 and/or F1+F2 to provide saidrepeated interrogation signal with frequency F2, and said repeatedinterrogation signal with frequency F2 emitted by the at least onerepeater RFID device and received by the at least one RFID transpondersupplies enough energy to said RFID transponder for the RFID transponderto emit said backscattered response signal with frequency F3.
 28. Asystem for electromagnetic interrogation of RFID transponders, thesystem comprising: at least one RFID transponder; at least one RFIDterminal comprising at least one RFID reader, the at least one RFIDterminal being configured to emit an interrogation signal at a frequencyF1; and at least one repeater RFID device configured to repeat, at afrequency F2 different from F1, said interrogation signal with frequencyF1, said repeated interrogation signal with frequency F2 being intendedfor being received by the at least one RFID transponder, wherein the atleast one RFID transponder is configured to emit a backscatteredresponse signal at a frequency F3 in response to receiving said repeatedinterrogation signal, in order to repeat, at a frequency F2, saidinterrogation signal with frequency F1, the at least one repeater RFIDdevice is configured to perform an exclusively analog frequencytransposition from the frequency F1 to the frequency F2, the at leastone repeater RFID device comprising a generator of reference signals andthe exclusively analog frequency transposition comprising mixing saidinterrogation signal with frequency F1 with a reference signal generatedby said generator of reference signals at a frequency F1−F2 and/or F1+F2to provide said repeated interrogation signal with frequency F2, andsaid repeated interrogation signal emitted by the at least one repeaterRFID at a frequency F2 includes a carrier configured to supply energy tothe at least one RFID transponder and an amplitude modulation of saidcarrier, said amplitude modulation being used to repeat saidinterrogation signal emitted by the at least one RFID terminal withfrequency F1.